In order to learn how visual excitation takes place, we plan to continue our investigations of the structure of the membrane of the rod outer segment and the biophysical and biochemical properties of the proteins which compose it. We feel that this research will prove significant not only to an understanding of the visual system, but also to our knowledge of the excitable membranes of all sensory systems. During the period of this grant, we intend to work on the following specific problems: purification of rod outer segments and their proteins including rhodopsin, the chemistry and photochemistry of these proteins, the structure of the rod outer segment, and mechanisms of visual excitation. Many of the techniques we will use will involve fluorescence of the rod outer segment, we will measure the distance between molecules inferred from fluorescence excitation measurements of the efficiency of energy transfer between them.